FINDER OPTICAL SYSTEM CAPABLE OF DIOPTER ADJUSTMENT

PURPOSE:To simplify the constitution and to improve the image performance by fixing 1st and 3rd lenses among three lenses constituting an ocular and moving a 2nd lens in the direction of the optical axis for diopter adjustment, and satisfying specific conditions. CONSTITUTION:The ocular L has the 1st negative lens L1, the 2nd positive lens L2, and the 3rd negative lens L3 in order from an observing eye side and the 2nd lens L2 is moved in the optical axis direction while the 1st and 3rd lenses are fixed, thereby performing the diopter adjustment. Then an inequality I holds. In the inequality I, f2 is the focal length of the 2nd lens L2, (f) the focal length of the whole finder system at the time of 0 diopter, N2 the refractive index of the 2nd lens L2, SF0 a shape factor showing the shape of the whole lens, r1 the radius of curvature of the lens surface of the ocular closest to the observing eye side, and r6 the radius of curvature of the lens surface closest to a focal plate side, so that expressions II hold. Consequently, the constitution is simplified and the image performance is improved.